Kostromateuthis Roemeri Gen

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A rare coleoid mollusc from the Upper Jurassic of Central Russia

LARISA A. DOGUZHAEVA

Doguzhaeva, L.A. 2000. Arare coleoid mollusc from the Upper Jurassic of Central Rus- sia. -Acta Palaeontologica Polonica 45,4,389-406. , The shell of the coleoid cephalopod mollusc Kostromateuthis roemeri gen. et sp. n. from the lower Kirnmeridgian of Central Russia consists of the slowly expanding orthoconic phragmocone and aragonitic sheath with a rugged surface, a weakly developed postalveolar part and a long, strong, probably dorsal groove. The sheath lacks concentric structure common for belemnoid rostra. It is formedby spherulites consisting of the needle-like crystallites, and is characterized by strong porosity and high content of originally organic matter. Each spherulite has a porous central part, a solid periphery and an organic cover. Tubular structures with a wall formed by the needlelike crystallites are present in the sheath. For comparison the shell ultrastructure in Recent Spirula and Sepia, as well as in the Eocene Belemnosis were studied with SEM. Based on gross morphology and sheath ultrastructure K. memeri is tentatively assigned to Spirulida and a monotypic family Kostromateuthidae nov. is erected for it. The Mesozoic evolution of spirulids is discussed.

Key words : Cephalopoda, Coleoidea, Spirulida, shell ultrastructure, Upper Jurassic, Central Russia. krisa A. Doguzhaeva [[email protected]], Paleontological Institute of the Russian Acad- emy of Sciences, Profsoyuznaya 123, 117647 Moscow, Russia.

Introduction The mainly soft-bodied coleoids (with the exception of the rostrum-bearing belemnoids) are not well-represented in the fossil record of extinct cephalopods that results in scanty knowledge of the evolutionary history of Recent coleoids and the rudimentary understanding of higher-level phylogenetic relationships of them (Bonnaud et al. 1997;Carlini & Graves 1999). Modern corntnonly accepted classification (Sweeney & Roper 1998) splits the coleoids into two superorders, the Decabranchia including the orders Spirulida, Sepiida, Sepiolida and Teuthida, and the Octobranchia including the orders Octopodida and Vampyromorphida. Because of its shell a single extant spirulid Spirula spirula has great potentialities for the evolutionary morphology of cephalopods. Voss (1977) considered this form as a member of the order Sepioidea, but later it was demonstrated with the aid of the mo-

Acta Palaeontol. Pol. 45,4,389-406. 390 Jurassic coleoid mollusc: DOGUZHAEVA

lecular phylogenetic analysis that Sp. spirula is linked neither to sepioids nor to teuthoids (Bonnaud et al. 1997; Carlini & Graves 1999). The evolution of spimlids is obscure, thus any shell found which might have belonged to this branch of coleoid cephalopods is of exceptional interest. The Jurassic record of spirulids included a single Oxfordian form Plagioteuthis moscoviensis Roemer, 1890 (see Biilow-Trumrner 1920). It is known by a sole rostrum-llke structure with a deep alveolus and had no indications of conotheca, septa or siphuncle. Because of this the taxonomic assignment of the genus remains doubtful (Doyle et al. 1994). The present paper deals with a better preserved shell belonging to a previously unknown Early Kimmeridgian phragmocone-bearing orthoconic coleoid with a sheath-like structure instead of a real rostrum. It is described herein as Kostro- mateuthis roemeri gen. et sp. n. The sheath ultrastructure of K. roemeri studied with SEM yielded much new information concerning the ultrastructure of the coleoid shell that is useful for the comparison of K. roemeri, spimlids, sepiids, and belemnoids.

Materials and methods

The description of Kostromateuthis roemeri is based on a shell from the lower Kimmeridgian clay beds in the basin of the River Unzha, on its right bank near village Popovo, Kostroma Region, Central Russia. It was found together with several ammonites by a private collector, Mr. A.V. Stupachenko in 1998. V.V. Mitta (personal com- munication) assigned the ammonites to the following species: Amoeboceras (Amoe- bites) ex. gr. kitchini, A. (A.) pulchrum, Prorasenia aff. stephanoides, and Rasenio- ides? sp. juv. The ammonoid assemblage indicates the standard Cymodoce Zone of the lower Kimmeridgian (Hantzpergue et al. 1998). The specimen was studied with the scanning electron microscope (SEM) in the PaleontologicalInstitute, Moscow. The micrographs were taken from the side showing the longitudinal groove and of the conical apical portion of the sheath; the latter being studied in fractured cross surface and from its outer surface. For comparison, the ultrastructure of the sheath of Recent Spirula from Cuba, Sepia from Australia, and Belemnosis from the Eocene of Turkey was studied with the SEM. The shells were etched with 5 per cent hydrochloric acid for 3-5 seconds. The studied material is deposited in the Paleontological Institute of the Russian Academy of Sciences, Moscow, abbreviated as PIN.

Description Class Cephalopoda Cuvier, 1794 Subclass Coleoidea Bather, 1888 Superorder Decabranchia Boettger, 1952 ?Order Spirulida Pompeckj, 1912 Family Kostromateuthidae nov. Type genus by monotypy: Kostromateuthis nov. ACTA PALAEONTOLOGICA POLONICA (45) (4) 391

Diagnosis. -Small (approximately 24cm in length) aragonitic orthocones, slowly expanding with bilaterally symmetrical sheath instead of rostrum. Sheath posteriorly conical; postalveolar portion absent or short; surface uneven; consisting of spherulites with much organic matter; thin (presumably) ventrally, thickened dorsally with the longitudinal central narrow part, which is thicker than elsewhere, bearing a groove, dorsally. The groove long, deep, bordered by two reinforced ridges with rows of tubercles along their crests and few smaller ridges on its floor. Phragmocone with simple camerae and straight septa; mural parts of septa long (about 113-215 of camera length); sutures non-sinuous. Occurrence. -Upper Jurassic, lower Kimmeridgian; Unzha River, Kostroma Region, Central Russia. Remarks. -The groove on the sheath is an apomorphy of the new family and distinguishes it from the older (Stephanian) family Shimanskyidae Doguzhaeva, Mapes, & Mutvei, 1998 and younger (Cretaceous) families Adygeyidae Doguzhaeva, 1996 and Groenlandibelidae Jeletzky, 1966, which have smooth shells, lacking grooves. The family is tentatively referred to the Order Spirulida on the basis of the following common features: well developed slowly expanding phragrnocone with comparatively short camerae, simple sutures, and septa with long mural parts; presence of a sheath with uneven surface and spherulitic ultrastmcture instead of a real rostrum. The protoconch structure, namely: whether it had a closing membrane as in belemnoids, or a calcified first septum with a septa1 foramen, a caecum and a prosiphon as in spirulids, is so far unknown. But the family can hardly be referred to belemnoids because of the dimpled surface of the sheath which is a resull or ils spherulitic structure. Among belemnoids, the new family resembles diplobelids in having no postalveolar portion of the rostrum. However, diplobelids have breviconic phragmocones, sinuous sutures and crowded septae (Jeletzky 1981: p. 115), unlike the new family. The reconstruction of the shell orientation is based on the fact that in coleoids the ventral side of the shell gradually lost its protective function and was replaced by a muscular mantle wall. For this reason the thickened side that bears the groove is considered as dorsal. Genus Kostromateuthis nov. Type species by monotypy: Kostromateuthis roemen' gen. et sp. n. Derivation of name: From Kostroma, the capital of the region where the specimen was found.

Diagnosis. - Miniature orthocones with angle of expansion 18-20 degrees. Sheath conical with rounded apex and irregular rows of bean-shaped depressions apically, and smoother, 'pock-marked' adorally. Groove bordered by two ridges with rows of more than 10 tubercles along their crests; two or three smaller ridges on its floor. Remarks. -In the uneven outer surface the sheath of Kostromateuthis is similar to partitions of the sheath of the Tertiary spirulid Beloptera (Dauphin k985: fig. 3f) and the outer surface of the sheath of Belemnosis. Also the tubercles along the crests flanking the groove show similarity to the humps on the outer surface of a longitudinal partition of the Beloptera sheath (Dauphin 1985: fig. 4a). These were interpreted as unbroken spherulites (Dauphin 1985: p. 330). Spherulites with central depressions are known in the sheath of the Paleocene Belopterina (Dauphin 1986: pl. 2a-c). Kostromateuthis roemeri gen. et sp. n. Fig. 1A-D. Holotype: PIN 38711221 - the only specimen known. Type horizon: Upper Jurassic, lower Kimmeridgian. Type locality: Unzha River, right bank near village Popovo, Kostroma Region, Central Russia. Derivation of name: in honour of Ferdinand Roemer, who described the first Jurassic coleoid shell which might have belonged to the Spirulida. Diagnosis. - Same as for genus. 392 Jurassic coleoid mollusc: DOGUZHAEVA ACTA PALAEONTOLOGICA POLONICA (45) (4) 393

Description. - The shell is small (24 mm long, with maximum diameter about 8 mm), orthoconic, slowly expanding (angle of expansion 18-20 degrees), surface uneven, especially in its apical part where it is reticulated. Phragmocone and sheath seem to be of equal length; sheath probably ends near the apertural margin of the phragmocone and does not extend beyond the phragmocone. The sheath bears a strong medial, presumably dorsal, groove bordered by two ridges with rows of tubercles along their crests and has two or three smaller ridges on its floor. The length of the groove is approximately 314 of the shell length, or maybe longer. Adorally the sheath is thin but near the groove it is thicker. Apically the sheath is conical with a rounded apex; here the outer surface exhibits irregular rows of bean-shaped depressions oriented perpendicular to the longitudinal axis of the shell. In the adoral direction the bean-shaped depressions give way to a 'pock-marked' pattern and the surface becomes smoother. The phragmocone consists of approximately 25-30 camerae; sutures straight; mural parts of septa are long; their length is about 113-215 of the camera length. The conotheca (Fig. ID) is as thin as a septum. Siphuncle and protoconch are unknown.

Shell wall ultrastructure of Kostromateuthis, Belemnosis, Spirula, and Sepia

Kostromateuthis. - The sheath is the only part of the shell studied with SEM, as the conotheca that was observed with the light microscope on the surface of the phragmocone, illustrated on Fig. 1A, was accidentally destroyed during the preparation of the specimen. The conotheca (Fig. 1D) looks like a thin white layer. The septa were not studied with SEM because they were badly crushed. Under the light microscope they show nacreous lustre. The sheath consists of spherulites formed of long thin crystallites of aragonite (Figs. 2A-D, 3A, B, 4A, B). The structure of the sheath changes remarkably from the apex towards the aperture, the apical portion of the sheath being more uneven than the adoral one (compare Fig. 1B and D). Close to its apical end the sheath contains many loosely packed spherical spherulites, each encased in an organic cover (Fig. 2A, B). Spaces between them probably were originally filled with organic matter. The spherulites exposed on the outer surface of the sheath exhibit a complex structure. Their central part is a porous crater-like depression while the periphery is a crest-like solid barrier separating adjacent spherulites (Figs. 2C, D, 3A, B). As a result the sheath has a rough, uneven surface with a 'pock-marked' pattern (Fig. lB, C). The centres of the spherulites are less calcified than their periphery (Fig. 2A, B) and probably originally contained organic matter as well. The spherulites exhibit growth lines (Fig. 2D) indi- cating periodic accretionary growth. The outer surface of the conical portion of the sheath, and probably the entire surface of the sheath, has a covering that seems to rep- resent an originally organic covering (Fig. 4A). Towards the aperture, the spherulites become more compactly arranged. In places where the originally organic covering is destroyed, numerous tiny tubular structures, terminated by pore openings, are exposed

Fig. 1. Kostromateuthis roemeri, PIN 38711221; lower Kimmeridgian; Unzha River, Kostroma Region, Central Russia. A. Presumably ventral view of the adoral portion of the preserved phragmocone, partly coated by a thin sheath, x 7. B. The opposite side of the sheath than in C, to show reniformed pattern on its surface; SEM micrograph; scale bar 0.3 mm. C. Conical apical portion of the sheath with uneven surface, rounded apex, and clearly visible alveola, x 10. D. Presumably dorsal view of the shell showing strong medial groove of the sheath, its undeformed thick dorsal and thin dorso-lateral portions, and the fragment of a thin conotheca (to the right), x 10. 394 Jurassic coleoid mollusc: DOGUZHAEVA

Fig. 2. Kostromateuthis roemeri, PIN 38711221. A. The sphemlites at the sheath apex; some sphemlites are spherical (note their size differences) and coated by the originally organic capsule; others are hemispherical -+ ACTA PALAEONTOLOGICA POLONICA (45) (4) 395 on the outer surface of the sheath (Fig. 4B). The walls of the tubes are formed by long thin crystals of aragonite parallel to the axis of the tube (Fig. 4C). Thus, strong porosity and high content of original organic matter seem to be characteristic features of the sheath of Kostromateuthis.

Belemnosis. - This Eocene genus is referred either to spirulids (Biilow-Trumrner 1920; Doyle et al. 1994; Haas 1997; Doguzhaeva 2000) or to sepiids (Naef 1922; Krimgolts 1958; Jeletzky 1966). The protoconch is ovoid with a slightly curved axis and the phragmocone is gently curved as well so that the axis of the latter is a continuation of the former. The convex side is presumably dorsal and the concave side is presumably ventral (Fig. 6C). The sheath is bilateraly symmetrical with widely conical apical portion; it is swollen and short on the (presumably) ventral side, while thin and long on the opposite one (Fig. 6C). The axis of the sheath does not concur with those of the protoconch and phragmocone. The side of the sheath whlch is almost perpendicular to the axis of the protoconch is straight (in medial section); here the thickness of the sheath is less than in front of the lateral side of the protoconch. The swollen part of the sheath shows large, loosely packed spherulites with central hollow spaces. Here the spherulites are formed by long thin crystallites. The apical part shows radial sectors (Fig. 6C) which have also been reported in the sheath of the Eocene Belopterina (Dau- phn 1986: fig. 4). Adorally, on the convex side of the phragmocone there are two distinctly separated spherulitic-prismaticplates (Fig. 6C). The outermost plate is formed by the spherulites consisting of needle-like prisms and separated by the organic membranes. The tubular structures with the openings visible as numerous black spots are present here (Fig. 6D). The conotheca is a thin prismatic layer. SpiruZa. -The shell wall of Recent Spirula (Fig. 5A, B) consists of two distinctly separated acicular-prismatic layers, termed the outer and inner plates (Appellof 1893). The clear separation of the two plates is due to the thick layer of connecting tissue which is attached to the outer surface of the inner plate near the aperture, where the outer plate is absent as it is secreted just after the attachment place of connecting tissue (Chun 1898-1899: p. 335). The inner plate is an acicular-prismatic layer showing strongly oblique growth lines which make an angle of about 25 degrees with the inner surface (Doguzhaeva 1996: text-fig. 3a-c; figs. 2,3). This indicates that the inner plate was secreted by the epithelium of the shell sac lining the inner surface of the last cham- ber. This acicular-prismatic layer shows alternations of black and white bands perpendicular to the growth lines and oblique to the shell surfaces (Doguzhaeva 1996: fig. 2). It is composed of prisms with a dendritic structure, a feather-like arrangement of acicular crystallites forming each prism (Doguzhaeva 1996: fig. 3). This layer seems to be rich in organic matrix that fills numerous narrow spaces between the crystallites and bundles of crystallites. with hollow centres; the spherulites are formed by the needle-like crystallites; scale bar 0.3 mm. B. Closc- up of A to show the organic cover and needle-like crystallites of the spherulites; scale bar 0.1 mm. C. The complex structure of the spherulites of the conical portion of the sheath, closer to the adoral portion of the shell where the sphemlites are compactly arranged; their periphery is a solid crest-like barrier and the central part is porous depression; scale bar 0.3 mm. D. Fracture of the solid crest-like periphery of the spherulites showing needle-like prisms and their growth lines exhibiting their periomcal secretion; scale bar 0.3 mm. SEM micrographs. 396 Jurassic coleoid mollusc: DOGUZHAEVA

Fig. 3. Kostromateuthis roemeri, PIN 38711221. A. The uneven surface of the sheath with 'pock-holes' which are central depressions of the spherulites surrounded by solid ridges; scale bar 0.1 rnm. B. The crest-like solid barrier separating two adjacent sphemlites; the central depressions are less calcified than their periphery and show numerous tubes; scale bar 0.03 mm. SEM micrographs. The intermediate layer between the two plates is thin, lamellar and is only weakly calcified, consisting predominantly of organic matrix (Fig. 5B). The outer plate is rep- resent by two layers: a thin acicular-prismatic layer and an outer coating layer (Fig. 5B). The acicular-prismatic layer has a simple prismatic structure consisting of acicular crystallites which are oriented more or less perpendicular to the layer bound- ACTA PALAEONTOLOGICA POLONICA (45) (4) 397 aries (Doguzhaeva 1996: fig. 3). The growth lines are uneven, more or less parallel to the shell surface. The coating layer covers the protoconch and forms the ventral ridge that is distinctly developed in the first whorl. The structure of the ventral ridge is strongly irregular, showing numerous interruptions of the oblique growth lines, result- ing in a lenticular pattern. At the end of the first whorl it looses its ridge-like shape. The coating layer represents a lateral and dorsal continuation of this ventral ridge. It is absent in the apertural region and last appears at the penultimate camera. During ontog- eny the coating layer grows proportionally thinner. It has a simple prismatic structure similar to that of the underlying layer; the growth lines are uneven, more or less parallel to the shell surface. The layer has a reticulate ridged outer surface.

Sepia. - The dorsal shield of the cuttle-bone shows an uneven outer surface and is formed by a thin laminated layer (the inner portion of the sheath) and a thick spherulitic-prismatic layer (the outer portion of the sheath). The former consists of several laminae more or less parallel to the inner surface of the sheath; the latter is formed by lens-like spherulites, which are composed of short acicular-prismatic crystallites. The spherulites are coated by thin organic films which separate them. The spine proper differs strongly from the rest of the sheath and does not seem to be a continuation of any of the layers of the sheath. It shows thin longitudinal laminations, granular structure between probably organic laminae, and numerous pores (Fig. 6A, B). Along the periphery there is a porous zone lacking growth lines. It is formed by the needle-like prisms and tubular structures of similar thickness, and with openings visible as numerous black spots like those in the sheath of K. roemeri (compare Fig. 6B and Fig. 4B).

Comparisons. - The sheath of Kostromateuthis is similar to that of spirulids and sepiids in being formed of spherulites consisting of thin long needle-like crystallites. As in Kostromateuthis, in Belemnosis and Sepia the sheath possesses tubular structures, the walls of which are formed by the needle-like crystallites as well. Among Ter- tiary sepiids the spherulitic-prismatic structure of the sheath has been observed in Belosepia, Beloptera, and Belopterina (Dauphin 1984, 1985, 1986). In contrast to these, the belemnites exhibit concentric structure of the rostrum, with radial prisms in each concentric growth ring. The diplobelids differ from all the other belemnoids and show a modified structure of the rostrum (Zittel1868; Jeletzky 1966,1981; Drushchits et al. 1984). The dimpled surface of the sheath of the K. roemeri gen. et sp. n. also contrasts with the mainly smooth, or in rare cases weakly ornamented, rostrum of belemnoids. These differences are a result of the complex spherulitic structure of the sheath in Kostro- mateuthis and the radial-prismatic structure of the rostrum in belemnites. It should be noted that some fully-grown belemnoid rostra are coated by a layer of coarse prismatic structure (the epirostrum) slightly similar to the outer plate of the sheath of sepiids, or spirulids. In these forms the outer surface is not smooth but rather pitted; however, this feature seems not to be a general character of belemnoids. Thus, the spherulitic-prismatic ultrastructure of the sheath of Kostromateuthis, taken separately, does not indicate affinity with any taxon of coleoids. Nevertheless, combination of features such as a fully developed phragmocone, comparatively short camerae, long mural parts of septa and simple sutures, strong fusion of septa and shell 398 Jurassic coleoid mollusc: DOGUZHAEVA ACTA PALAEONTOLOGICA POLONICA (45) (4) 399

Fig. 5. Recent Spirula, PIN 38711134; Cuba. Medial section of the shell wall consisting of outer and inner plates with the intermediate later between them at a young (A) and late (B) ontogenetic stages. The plates show acicular-prismatic ultrastructure, the intermediate layer is irregularly calcified organic; the inner plate is thin and the outer plate is thick at the beginning (A) and vice versa later (B); scale bars 0.1 mm. SEM micrographs. wall, uneven surface of the sheath which is often bilaterally symmetrical, and the ab- sence of a nacreous layer in the shell wall (Doguzhaeva 1996,2000; Doguzhaeva et al. 1998), suggests spirulid affinity of Kostromateuthis.

The Mesozoic evolution of spirulids and sepiids

Judging by the external appearance of the shell, K. roemeri could be assigned to belemnotheutids which are "a 'catchall' for most, or all, late Paleozoic and Mesozoic

Fig. 4. Kostrornateuthis roemeri, PIN 38711221. A. The surface, longitudinal and transverse fractures of the conical portion of the sheath to show the dark spots which are covered by presumably organic matter and the light ones which are porous and lack the organic covering; the transverse fracture (left side) shows the central cavities of the two sphemlites and the radial needle-like prisms; the longitudinal fracture shows in- clined prisms of the sphemlites; scale bar 0.1 rnm. B. The exposed porous area of the sheath surface showing numerous pores and tubular strnctures; the places where the pores are not visible are coated by presumably originally organic matter; scale bar 0.1 mm. C. Close-up of B showing three distinct tubular structures; their wall is formed by long, thin needle-like prisms; scale bar 0.01 rnm. SEM micrographs. 400 Jurassic coleoid mollusc: DOGUZHAEVA

Fig. 6. A, B. Longitudinal section of cuttle-bone of Recent Sepia; PIN 38711216; Australia. A. The spine showing the growth lines recording the ontogenetic changes of its shape and its high porosity; scale bar 0.1 mm. B. Close-up of A; the longitudinalperipheral porous zone of the spine showing numerous black spots which seem to be the openings of the tube-like structures like those in the sheath of K. roemeri (compare with ACTA PALAEONTOLOGICA POLONICA (45) (4) 40 1

belemnite-like coleoids characterized by relatively weakly developed guards" (Jelet- zky 1966: p. 144), or to the diplobelids. However, the belemnotheutids have the typical belemnoid concentric structure of the rostrum (Makowski 1952; Bandel & Kulicki 1988); in diplobelids the sutures are more sinuous than in any other belemnoids, with a pronounced dorsal saddle and a weak ventral saddle, and the septa are usually consid- erably crowded (Jeletzky 1966, 1981), which is not the case in K. roemeri. The idea of the possible existence of Jurassic sepiids was introduced by Roemer (1890) who described Plagioteuthis moscoviensis from the Oxfordian of Central Rus- sia. The sole available specimen of this form is represented by a small (4 cm in length) slightly curved asymmetrical sculptured rostrum with deep slowly expanding alveola; one side of the rostrum is thicker than the other. Roemer compared Plagioteuthis with Belosepia, Spirulirostra, and Diploconus and believed that it belonged either to Belosepiidae, Belopteridae, or Belemnitidae (Roemer 1890: p. 362). Kostromateuthis confirms Bulow-Trummer's idea (1920) of combining the Late Jurassic Plagioteuthis with Tertiary genera such as Belemnosis, Beloptera, Belo- pterina, Spirulirostra, Spirulirostrina, and Vasseuria in the family Spirulidae, thus extending the lineage of the spirulids back to the Late Jurassic. However, Krimgolts (1958) considered Plagioteuthis as a conventional member of Belemnosidae. Naef (1922) and Jeletzky (1966) did not index Plagioteuthis. Doyle et al. (1994) listed it as incertae sedis. Nevertheless, several decades later the discovery of a caecum and a prosiphon within the protoconch of the Maastrichtian Groenlandibelus rosen- krantzi, which has a superficially belemnotheutid appearance, provided strong evi- dence that the spirulid lineage existed in the Late Cretaceous (Jeletzky 1966). The finding of the Aptian Naefia kabanovi extended it to the Early Cretaceous (Dogu- zhaeva 1996). Bulow-Trummer (1920) grouped the forms with normal phragmocones in the Suborder Phragmophori (Belemnoidea, Belemnotheutidae, and Spirulidae) and separated them from the Suborder Sepioidei which included sepiids as well as teuthids. The idea of keeping the forms with fully developed phragmocones separate still seems to be acceptable. In light of this view the record of fossil spirulids probably includes, in addition to the six Tertiary genera mentioned above, the following: the Stephanian Shimanskya of the USA Mid-Continent (Doguzhaeva et al. 1998), the Aptian-Maastrichtian Naefia of Chile, India, Antarctica, Japan and the Caucasus (Wetzel 1930; Biro-Bagoczky 1982; Stinnesbeck 1986; Doyle 1986; Stilwell & Zinsmeister 1987; Hewitt et al. 1991; Doguzhaeva 1996), the Aptian Adygeya of the North-Western Caucasus (Doguzhaeva 1996), the Maastrichtian Groenlandibelus of West Greenland (Jeletzky, 1966) and the Miocene Spirula

Fig. 4B); scale bar 0.01 mm. C, D. Belemnosis sp.; PIN 38711140; Eocene, Turkey; medial shell section. C. The ovoid protoconch and approximately 10 first camerae of the phragmocone; the curved axis of the phragmocone is a continuation of the curved axis of the protoconch; the sheath is bilateraly symmetrical: on the concave (presumably ventral) side of the phragmocone it is short and swollen, and on the convex (presumably dorsal) side it is thinner and longer that on the opposite one; the post-alveola portion is short; the reticulate pattern of the sheath is well visible in the swollen part; scale bar 0.1 rnm. D. Close-up of C to show the differently oriented needle-like prisms and similarly thin tubular structures of the outermost portion of the sheath on the convex side of the phragmocone; the organic membranes separating adjoining spherulites are partly preserved; scale bar 0.01 mm. 402 Jurassic coleoid mollusc: DOGUZHAEVA mizunamiensis of Japan (Tomida & Itoigawa 1981). In the genera from this list, a spherical protoconch has so far been observed in Groenlandibelus (Jeletzky 1966), Belemnosis (Doguzhaeva 2000; herein) and Spirula mizunamiensis (Tomida & Itoigawa 1981). The caecum and prosiphon have been documented only in Groen- landibelus shell but they are still believed to be the characters of spirulids distin- guishing their shells from those of diplobelids and other belemnoids. The view that the spirulids (and sepiids) evolved from the belemnoid stock is still widespread (Dauphin 1985; Teichert 1988; Meyer 1993; Hewitt & Jagt 1999), but it is also widely questioned (Jeletzky 1966; Engeser & Bandel 1988; Doyle et al. 1994; Doguzhaeva 1996; Doguzhaeva et ~1.1998).The origin of spirulids via reduc- tion and loss of a rostrum in belemnoid-like ancestors was introduced by Volz (1830), supported by Schwarz (1895) and significantly elaborated by Naef (1922). Hewitt & Jagt (1999: p. 323) still believe that the spherulitic ultrastructure of the sheath in Belosaepia and Sepia was inherited from that of diplobelids. It has been known since Zittel(1868) that diplobelids apparently lacked the radially prismatic structure of the rostrum. According to Hewitt & Jagt (1999: p. 324), 'separate ori- gins of the Sepiida and Spirulida within the Cretaceous diplobelid belemnites is still the most attractive hypothesis, until the case for pre-Aptian fossil record of spirulids becomes overwhelming.' The available data on ultrastructure of the rostrum in diplobelids is so far scarce. Jeletzky (1981: p. 115) characterized the diplobelinid belemnites as having a tapering pro-ostracum with an acute or very narrowly rounded tip and hyperbolar zones of belemnitid type; suture lines more sinuous than in any other belemnitids, with a pronounced dorsal saddle and a small ventral lobe; crowded septa (the height of camera up to one-twentieth of their length); a usually breviconic phragmocone with the apical half curved endogastrically; and a rudimentary or short, stout, and apically bluntly rounded rostrum. Jeletzky (1966: p. 149) had noticed that, unlike in the other suborders of Belemnitida, the rostrum of diplobelids generally lacks radial-prismatic structure. However, after restudy and revision of a large collection of diplobelids, Jeletzky (198 1: p. 116) concluded that 'apparent lack of the radially prismatic structure of the guard appears to be a result of post-mortem weathering in those forms where it is re- duced to a very thin ... envelope.' In Conoteuthis dupiniana the rostrum has a smooth surface and shows radial striation suggestive of its primary radial-prismatic structure (Jeletzky 1981: p. 126). In the Early Cretaceous Pavloviteuthis the rostrum exhibits belemnitid-like radial-prismatic structure (Jeletzky 1981: p. 127). Nevertheless, in the Aptian Chalalabelus he showed the rostrum with lamellar structure (Jeletzky 1981: text-fig. 12a). Drushchits et al. (1984) studied the rostrum ultrastructure of the Valan- ginian diplobelid Tauriconites nikolai Kabanov, 1980. In this form the surface of the rostrum reflects the undulations of the phragmocone surface (Druschits et al. 1984: fig. 2a) and shows transverse ridges and grooves on the ventral side. Similar undulations of the phragmocone surface are also known in Recent Spirula and in Naefia. These authors raised the diplobelids to the rank of Order Diplobelida Jeletzky, 1965 on the basis of differences in the structure of the rostrum between belernnoids and diplobelids. The apical portion of the rostrum in Tauriconites consists of spherulites re- sulting in a pattern of sectors in median section (Doguzhaeva, unpublished data) similar to that of several Tertiary sepiids (Dauphin 1984: fig. 6f, 1986: pl. 2d). However, ACTA PALAEONTOLOGICA POLONICA (45) (4) 403 the anterior part of the rostrum exhibits concentric growth lines and a radial arrangement of short prismatic crystals more like the radial-prismatic structure of ordinary belemnite rostra. Thus, there are essential differences between the structure of the sheath of K. roemeri and the rostrum of diplobelids that exclude the new form from Diplobelidae. Finally, following the idea of the inheritance of the spherulitic structure of the shell by the Tertiary sepiids and spirulids from their ancestors, one might expect that they evolved from the early Kimmeridgian Kostromateuthis-like forms rather than from the diplobelids which appeared in the Tithonian, later than Kostromateuthis. More probably, however, they inherited their ultrastructural characters from more remote still unknown precursors. The Stephanian Shimanskya postremus Doguzhaeva, Mapes & Mutvei, 1998 is the only older spirulid known so far. Being longiconic and having no grooves, the shell of this form has an external appearance that is essentially bactritid- like. However, contrary to bactritoids but similar to spirulids Sh. postremus lacks a nacreous layer in the shell wall (Doguzhaeva 1996; Doguzhaeva et al. 1998) which is porous, formed by the inner and outer prismatic plates. Thus, the Lower Carboniferous decapods probably were represented at least by the three orders: Aulacocerida (Shi- mansky 1960), Spirulida (Doguzhaeva et al. 1998), and Hematitida (Doguzhaeva et al. in press), that confirmes the idea on a rapid radiation in evolution of decapods (Bonnaud et al. 1997).

Acknowledgements

The private collector A.V. Stupachenko (Moscow) collected and donated to the Paleontological Insti- tute in Moscow the specimen described herein as Kostromateuthis roemeri, V.V. Mitta (All-Russian Research Geological Oil Institute, Moscow) identified the ammonites found with the described specimen and on this basis established the lower Kimrneridgian age of the finding, V.T. Antonova (PIN) took the light microscope photos (Fig. lA, C, and D), and T.A. Grunt (PIN) collected and donated the specimen of Sepia from Australia. D.T. Donovan (University College, London) and H. Mutvei (Swedish Museum of Natural History, Stockholm) read an earlier version of this paper and provided linguistic corrections. M. Vecchione (National Museum of Natural History, Srnithsonian Institution), Ch. Spaeth (Geological-Paleontological Institute and Museum, Hamburg University), and N.H. Landman (Department of Invertebrates, American Museum of Natural History) reviewed this paper and provided helpful comments. To all these persons I express my sincere thanks and gratitude.

References

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